1. Field of the Invention
The present invention relates to liquid-crystal display devices and more particularly to a liquid-crystal display device having a semiconductor device of so-called a tape carrier scheme as its drive circuit.
2. Description of the Related Art
The liquid-crystal display device of so-called an active-matrix type is structured to sequentially select the pixel columns by turning on the thin-film transistors provided at the pixels thereof according to a scanning signal supplied through the signal line and to supply, in timing with such selection, a video signal to the pixels of the relevant pixel column through the drain signal lines commonly connected to the corresponding pixels of the other pixel columns when driving the pixels of the liquid-crystal display panel.
For this reason, a scanning-signal drive circuit having a plurality of juxtaposed semiconductor devices is provided at the orthogonal side of the liquid-crystal display panel to the gate signal lines while a video-signal drive circuit having a plurality of juxtaposed semiconductor devices is provided at the orthogonal side of the liquid-crystal display panel to the drain signal lines.
As the semiconductor devices of the scanning-signal and video-signal drive circuits, there is known a structure using a semiconductor device of so-called a tape carrier scheme. The tape-carrier-schemed semiconductor device is structured by mounting a semiconductor chip on a flexible board and leading the terminals of the semiconductor chip to the periphery of the flexible board through lines.
Such a semiconductor device can be electrically connected to the corresponding terminals by connecting the flexible board at its one side portion to a part of the periphery of the liquid-crystal display panel. By bending the semiconductor device thus connected to the liquid-crystal display panel at its flexible-board portion in a manner being directed vertically to the surface of the liquid-crystal display panel, effects are to be enjoyed including so-called edge reduction.
Meanwhile, besides the scanning signal and the video signal, there is a need to supply a reference signal having a reference potential relative to those signals (hereinafter, referred to as a reference voltage signal in the present description), to the pixels of the liquid-crystal display panel. In such a situation, JP-A-2004-62201 (corresponding to U.S. Patent Application US2004/0017535), for example, discloses a technique to supply the reference voltage signal to the pixels of a liquid-crystal display panel through the lines formed on a flexible board of the semiconductor device.
Concerning the liquid-crystal display device structured as above, size increase and addressability improvement have been recently achieved in its liquid-crystal display panel. On the contrary, there arises a tendency toward decreasing the number of semiconductor devices constituting the video-signal and scanning-signal drive circuits in an effort to reduce the cost.
In this case, by reason of the increasing number of pixels with the addressability improvement of the liquid-crystal display panel, the number of terminals must be increased on the semiconductor device. Meanwhile, the reference voltage signal to be supplied to the pixels requires to be stably outputted in order for high-speed driving for the purpose of addressability improvement, size increase and moving-image quality improvement.
This is because of the reason that, where the reference voltage signal, to be supplied to the pixels, is not uniform and unstable in potential, electric field for moving the liquid-crystal molecules does not take place in a predetermined manner at each pixels thus causing poor image quality.
In order to stabilize the reference voltage signal to be supplied to the pixels of the liquid-crystal display panel, it can be considered to structurally supply a reference voltage signal to the liquid-crystal display panel through a multiplicity of distributed supply paths. However, this results in a disadvantage that the supply paths for the reference voltage signal are greatly reduced with the decreasing number of semiconductor devices.